Treatments to reduce frictional wear between components made of ultra-high molecular weight polyethylene and metal alloys

Abstract

The present invention provides methods for modifying surfaces made from metal alloy and/or UHMWPE, preferably surfaces which are frictionally engaged, e.g., in an orthopaedic implant. The methods of the present invention reduce the coefficient of friction of the metal alloy component, reduce the shearing of fibrils from the UHMWPE component, and reduce sub-surface fatigue in the UHMWPE component. The method involves solvent immersion of the UHMWPE component to remove short chains of polyethylene at or near the surface of the component, and to swell and toughen the subsurface of the component. The method also involves firmly coating the surface of the metal alloy component with an adherent layer of diamond-like carbon ("DLC") by creating a metal-silicide interface at the surface of the metal alloy to permit firmer adhesion of DLC. Although the methods of the present invention are particularly useful in orthopaedic applications, the methods also can be used to treat similar components used in other applications.

We claim: 
     
       1. A process for treating an ultra-high molecular weight polyethylene component to reduce frictional shearing off of fibrils from said component comprising: immersing said ultra-high molecular weight polyethylene component in an organic solvent for a first amount of time and at a temperature sufficient to dissolve polyethylene fibrils that are susceptible to frictional shearing off during use but insufficient to result in damage due to swelling of said ultra-high molecular weight polyethylene component, said organic solvent being selected from the group consisting of an aromatic hydrocarbon, an alicyclic hydrocarbon, an aliphatic hydrocarbon, and a mixture thereof; and   exposing said component to a vacuum of 10 -1  -10 -5  torr for a second amount of time sufficient to remove residual solvent.   
     
     
       2. The process of claim 1 wherein said first amount of time comprises at least 30 seconds. 
     
     
       3. The process of claim 1 wherein said second amount of time comprises at least 8 hours. 
     
     
       4. The method of claim 1 wherein said temperature is between about 30°-100° C. 
     
     
       5. The method of claim 1 wherein said temperature is between about 30°-50° C. 
     
     
       6. The method of claim 2 wherein said temperature is between about 30°-100° C. 
     
     
       7. The method of claim 2 wherein said temperature is between about 30°-50° C. 
     
     
       8. The method of claim 3 wherein said temperature is between about 30°-100° C. 
     
     
       9. The method of claim 3 wherein said temperature is between about 30°-50° C. 
     
     
       10. A method for making an orthopaedic implant comprising a metal alloy substrate in frictional contact with an ultra-high molecular weight polyethylene component, said method comprising the steps of: immersing said ultra-high molecular weight polyethylene component in an organic solvent for a first amount of time and at a temperature sufficient to dissolve polyethylene fibrils that are susceptible to frictional shearing off during use but insufficient to result in damage due to swelling of said ultra-high molecular weight polyethylene component, said organic solvent being selected from the group consisting of an aromatic hydrocarbon, an alicyclic hydrocarbon, an aliphatic hydrocarbon, and a mixture thereof;   exposing said component to a vacuum at a pressure of about 10 -3  torr for a second amount of time sufficient to remove residual solvent;   exposing a substrate comprising a metal alloy selected from the group consisting of cobalt, nickel, titanium, zirconium, chromium, molybdenum, tungsten, platinum, palladium, and combinations thereof, to a vacuum at a pressure of about 10 -5  torr or less;   heating said substrate to about 300° C. or, if said metal alloy is temperature sensitive, to a highest temperature acceptable for said metal alloy;   depositing silicon onto said substrate to a thickness of between about 100-200 nm;   substantially simultaneously bombarding said deposited silicon with a first energetic beam of nitrogen ions having a first energy of between about 10-30 keV at a first ion density and for a third amount of a time sufficient to form an inner bonding layer of metal-silicide cohesively bonded to an outer layer of silicon;   cooling said substrate to about 80° C.;   condensing a diamond-like carbon precursor onto said outer layer of silicon for a fourth amount of time sufficient to form a film of precursor molecules on said outer layer of silicon;   substantially simultaneously bombarding said diamond-like carbon precursor with a second energetic beam of nitrogen ions having a second energy of between about 10-30 keV at a second ion density and for a fifth amount of time sufficient to form a silicon carbide bonding layer cohesively bonded to an outer coating of diamond-like carbon.   
     
     
       11. A method for coating a metal alloy substrate with diamond-like carbon comprising: exposing said metal alloy substrate to a vacuum at a pressure of about 10 -5  torr or less;   heating said substrate to a first temperature of about 300° C. or, if said metal alloy is temperature sensitive, to a highest temperature acceptable for said metal alloy;   depositing silicon onto said substrate in an amount sufficient to form an inner bonding layer of metal-silicide cohesively bonded to an outer layer of silicon;   substantially simultaneously bombarding said deposited silicon with a first energetic beam of ions at a first energy, a first ion density, and for a first amount of time sufficient to form said inner metal-silicide bonding layer cohesively bonded to said outer layer of silicon;   condensing a diamond-like carbon precursor onto said outer layer of silicon at a second temperature and for a second amount of time sufficient to form a film of precursor molecules on said outer layer of silicon, wherein said second temperature is sufficiently low that said diamond-like carbon precursor is not vaporized off of said substrate;   substantially simultaneously bombarding said diamond-like carbon precursor with a second energetic beam of ions at a second energy, a second ion density, and for a third amount of time sufficient to form an inner silicon carbide layer cohesively bonded to an outer coating of diamond-like carbon.   
     
     
       12. The method of claim 11 wherein said first and second beam of ions comprise ions selected from the group consisting of nitrogen, argon, hydrogen, silicon, methane, helium, neon, and combinations thereof. 
     
     
       13. The method of claim 11 wherein said second beam of ions comprises nitrogen ions. 
     
     
       14. The method of claim 11 wherein said first energy and said second energy are between about 10-30 keV. 
     
     
       15. The method of claim 11 wherein said second temperature is about 80° C. 
     
     
       16. The method of claim 13 wherein said second temperature is about 80° C. 
     
     
       17. The method of claim 11 wherein said silicon is deposited onto said substrate to a thickness of between about 100-200 nm. 
     
     
       18. The method of claim 12 wherein said silicon is deposited onto said substrate to a thickness of between about 100-200 nm. 
     
     
       19. A method for coating a metal alloy substrate with diamond-like carbon comprising: providing a substrate comprised of a metal alloy selected from the group consisting of cobalt, nickel, titanium, zirconium, chromium, molybdenum, tungsten, platinum, palladium, and combinations thereof;   exposing said substrate to a vacuum at a pressure of about 10 -5  torr or less;   heating said substrate to a first temperature of about 300° C. or, if said metal alloy is temperature sensitive, to a highest temperature acceptable for said metal alloy;   depositing silicon onto said substrate in an amount sufficient to form an inner bonding layer of metal-silicide cohesively bonded to an outer layer of silicon;   substantially simultaneously bombarding said deposited silicon with a first energetic beam of ions at a first energy, a first ion density, and for a first amount of time sufficient to form said inner metal-silicide bonding layer cohesively bonded to said outer layer of silicon;   condensing a diamond-like carbon precursor onto said outer layer of silicon at a second temperature and for a second amount of time sufficient to form a film of precursor molecules on said outer layer of silicon, wherein said second temperature is sufficiently low that said diamond-like carbon precursor is not vaporized off of said substrate;   substantially simultaneously bombarding said diamond-like carbon precursor with a second energetic beam of ions at a second energy, a second ion density, and for a third amount of time sufficient to form an inner silicon carbide layer cohesively bonded to an outer coating of diamond-like carbon.   
     
     
       20. The method of claim 19 wherein said second beam of ions comprises nitrogen ions. 
     
     
       21. The method of claim 19 wherein said first energy and said second energy are between about 10-30 keV. 
     
     
       22. The method of claim 19 wherein said second temperature is about 80° C. 
     
     
       23. The method of claim 19 wherein said silicon is deposited onto said substrate to a thickness of between about 100-200 nm. 
     
     
       24. A method for making an orthopaedic implant comprising a metal alloy substrate in frictional contact with an ultra-high molecular weight polyethylene component, said method comprising the steps of: exposing a substrate comprising a metal alloy selected from the group consisting of cobalt, nickel, titanium, zirconium, chromium, molybdenum, tungsten, platinum, palladium, and combinations thereof, to a vacuum at a pressure of about 10 -5  torr or less;   heating said substrate to about 300° C. or, if said metal alloy is temperature sensitive, to a highest temperature acceptable for said metal alloy;   depositing silicon onto said substrate to a thickness of between about 100-200 nm;   substantially simultaneously bombarding said deposited silicon with a first energetic beam of nitrogen ions having a first energy of between about 10-30 keV at a first ion density and for a third amount of a time sufficient to form an inner bonding layer of metal-silicide cohesively bonded to an outer layer of silicon;   cooling said substrate to about 80° C.;   condensing a diamond-like carbon precursor onto said outer layer of silicon for a fourth amount of time sufficient to form a film of precursor molecules on said outer layer of silicon;   substantially simultaneously bombarding said diamond-like carbon precursor with a second energetic beam of nitrogen ions having a second energy of between about 10-30 keV at a second ion density and for a fifth amount of time sufficient to form a silicon carbide bonding layer cohesively bonded to an outer coating of diamond-like carbon.   
     
     
       25. A method for coating a metal alloy orthopaedic component with diamond-like carbon comprising: exposing said metal alloy orthopaedic component to a vacuum at a pressure of about 10 -5  torr or less;   heating said component to a first temperature of about 300° C. or, if said metal alloy is temperature sensitive, to a highest temperature acceptable for said metal alloy;   depositing silicon onto said component in an amount sufficient to form an inner bonding layer of metal-silicide cohesively bonded to an outer layer of silicon;   substantially simultaneously bombarding said deposited silicon with a first energetic beam of ions at a first energy, a first ion density, and for a first amount of time sufficient to form said inner metal-silicide bonding layer cohesively bonded to said outer layer of silicon;   condensing a diamond-like carbon precursor onto said outer layer of silicon at a second temperature and for a second amount of time sufficient to form a film of precursor molecules on said outer layer of silicon, wherein said second temperature is sufficiently low that said diamond-like carbon precursor is not vaporized off of said component;   substantially simultaneously bombarding said diamond-like carbon precursor with a second energetic beam of ions at a second energy, a second ion density, and for a third amount of time sufficient to form an inner silicon carbide layer cohesively bonded to an outer coating of diamond-like carbon.   
     
     
       26. The method of claim 25 wherein said second beam of ions comprises nitrogen ions. 
     
     
       27. The method of claim 25 whereto said first energy and said second energy are between about 10-30 keV. 
     
     
       28. The method of claim 26 wherein said first energy and said second energy are between about 10-30 keV. 
     
     
       29. The method of claim 25 wherein said silicon is deposited onto said substrate to a thickness of between about 100-200 nm. 
     
     
       30. A method for coating a metal alloy orthopaedic component with diamond-like carbon comprising: providing an orthopaedic component comprised of a metal alloy selected from the group consisting of cobalt, nickel, titanium, zirconium, chromium, molybdenum, tungsten, platinum, palladium, and combinations thereof;   exposing said component to a vacuum at a pressure of about 10 -5  torr or less;   heating said component to a first temperature of about 300° C. or, if said metal alloy is temperature sensitive, to a highest temperature acceptable for said metal alloy;   depositing silicon onto said component in an amount sufficient to form an inner bonding layer of metal-silicide cohesively bonded to an outer layer of silicon;   substantially simultaneously bombarding said deposited silicon with a first energetic beam of ions at a first energy, a first ion density, and for a first amount of time sufficient to form said inner metal-silicide bonding layer cohesively bonded to said outer layer of silicon;   condensing a diamond-like carbon precursor onto said outer layer of silicon at a second temperature and for a second amount of time sufficient to form a film of precursor molecules on said outer layer of silicon, wherein said second temperature is sufficiently low that said diamond-like carbon precursor is not vaporized off of said component;   substantially simultaneously bombarding said diamond-like carbon precursor with a second energetic beam of ions at a second energy, a second ion density, and for a third amount of time sufficient to form an inner silicon carbide layer cohesively bonded to an outer coating of diamond-like carbon.   
     
     
       31. The method of claim 30 wherein said second beam of ions comprises nitrogen ions. 
     
     
       32. The method of claim 30 wherein said first energy and said second energy are between about 10-30 keV. 
     
     
       33. The method of claim 31 wherein said first energy and said second energy are between about 10-30 keV. 
     
     
       34. The method of claim 30 wherein said silicon is deposited onto said substrate to a thickness of between about 100-200 nm. 
     
     
       35. A process for treating an ultra-high molecular weight polyethylene orthopaedic component to reduce frictional shearing off of fibrils from said component comprising: immersing said ultra-high molecular weight polyethylene orthopaedic component in an organic solvent for a first amount of time and at a temperature sufficient to dissolve polyethylene fibrils that are susceptible to frictional shearing off during use but insufficient to result in damage due to swelling of said ultra-high molecular weight polyethylene orthopaedic component, said organic solvent being selected from the group consisting of an aromatic hydrocarbon, an alicyclic hydrocarbon, an aliphatic hydrocarbon, and a mixture thereof; and   exposing said component to a vacuum of 10 -1  -10 -5  torr for a second amount of time sufficient to remove residual solvent.   
     
     
       36. The process of claim 35 wherein said first amount of time comprises at least seconds. 
     
     
       37. The process of claim 35 wherein said second amount of time comprises at least 8 hours. 
     
     
       38. The process of claim 36 wherein said second amount of time comprises at least 8 hours.